This invention relates to apparatus and methods for power quality measurement. In particular, this invention relates to apparatus and methods for detecting and measuring characteristics of dips, swells and interruptions in AC power systems.
Voltage dips, swells, and interruptions are short-duration disturbances in AC power systems (referred to herein as “DSI Disturbances”). Voltage dips are brief reductions in voltage magnitude lasting anywhere from milliseconds to a few seconds. Voltage swells are brief increases in voltage magnitude lasting anywhere from milliseconds to a few seconds. Voltage interruptions are more severe decreases in voltage magnitude. The threshold for voltage interruptions is usually less than 10% of nominal voltage.
Various industry standards define characteristics of DSI Disturbances, and also specify methods to measure the duration and magnitude of DSI Disturbances. However, the power line frequency (e.g., 60 Hz in the US, and 50 Hz in Europe) may vary by ±15% of nominal, which makes it very difficult to accurately detect and measure characteristics of DSI Disturbances. Accordingly, improved systems and methods for detecting and measuring characteristics of DSI Disturbances are desirable.